Allelopathic potential of invasive parthenium weed (Parthenium hysterophorus L.) seedlings on grassland species in Australia

The allelopathic nature of adult Parthenium hysterophorus L. (parthenium weed) plants, suppressing the growth and development of its near neighbours, has been implicated in its success as an important invader around the world. This study for the first time, evaluates the allelopathic potential of parthenium weed seedlings, comparing its impacts upon seven introduced and four native Australian grassland species using the ‘plant box’ method (10). Results showed a species-specific response, often with the growth of native species being more affected than introduced species and root growth more affected than shoot growth. The native grasses [curly windmill grass (Enteropogon acicularis L.; 59% inhibition) and cotton panic grass (Digitaria brownii L.; 54% inhibition)] were the most affected, while the introduced [Rhodes grass (Chloris gayana L.; 0% inhibition), buffel grass (Cenchrus ciliaris L.; 8% inhibition) and siratro (Macroptilium atropurpureum (DC.) Urb.; 9% inhibition)] were the least affected in their root growth. These results suggested that parthenium weed is capable of interfering with the growth of neighbouring seedlings even at very early stages of growth. The response found for buffel grass may partially explain why this introduced pasture grass has been found successful in suppressing the growth of parthenium weed in the field